>>>>
<excerpt>From: "Brian Straight"
To: ,
Subject: SETI New Scientist PR
Date: Thu, 24 Jun 1999 14:20:36 -0500
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EMBARGOED FOR RELEASE: 23 JUNE 1999 AT 14:00:00 ET US
Contact: Claire Bowles
<<mailto:claire.bowles@rbi.co.uk>claire.bowles@rbi.co.uk
44-171-331-2751
US Contact: New Scientist Washington office
<<mailto:newscidc@idt.net>newscidc@idt.net
202-452-1178
*New Scientist
If the Sun is exceptional, alien life may be hard to find
What a star!
**
Don't believe everything you read in books-our Sun is no ordinary star.
And
its very uniqueness has implications for SETI, the search for
extraterrestrial life, claims Guillermo Gonzalez of the University of
Washington in Seattle: "Unless astronomers narrow down their search to
stars as exceptional as the Sun, they are wasting much of their time."
The Sun is a single star whereas most stars are in multiple systems.
But
that apart, textbooks say the Sun is pretty average. However, after
trawling through the data on the Sun, Gonzalez has found many
idiosyncrasies. It is among the most massive 10 per cent of stars in
its
neighbourhood. It also has 50 per cent more heavy elements than other
stars
of its age and type, and about a third of the variation in brightness.
The most unusual aspects of the Sun concern its orbit around the centre
of
the Galaxy, says Gonzalez. Its orbit is significantly less elliptical
than
that of other stars of its age and type, and hardly inclined at all to
the
Galactic plane. What's more, the Sun is orbiting very close to the
"corotation radius" for the Galaxy-the place at which the angular speed
of
the spiral pattern matches that of the stars.
Gonzalez argues that these exceptional characteristics made it possible
for
intelligent life to emerge on Earth. He points out that stable
planetary
orbits such as the Earth's are much more likely around single stars
like
the Sun. For a massive star with inhabitable planets that are
relatively
far away, stellar flare-ups would be little threat to the planets.
Heavy
elements are essential to make planets like Earth, and a star with a
stable
light output is essential for life.
As for the orbit of the Sun, its circularity prevents it plunging into
the
inner Galaxy where life-threatening supernovae are more common. And its
small inclination to the Galactic plane prevents abrupt crossings of
the
plane that would stir up the Sun's Oort Cloud and bombard the Earth
with
comets. By being near the Galaxy's corotation radius, the Sun avoids
crossing the spiral arms too often, an event that would expose it to
supernovae, which are more common there.
Because life-bearing stars have to be close to the corotation radius,
that
rules out more than 95 per cent of stars in the Galaxy in one fell
swoop.
"There are fewer stars suitable for intelligent life than people
realise,"
says Gonzalez, who has submitted his findings to Astronomy &
Geophysics.
"I'm amazed at how little thought the SETI people put into selecting
their
stars."
Seth Shostak of the SETI Institute in Mountain View, California,
disagrees.
"Our targets are all very close to the Sun. They share our Galactic
neighbourhood and motions. If the Sun is the most suitable type of star
to
be scrutinised, then we are, indeed, looking in all the best places."
"Most astronomers disagree with Gonzalez," adds SETI researcher Dan
Werthimer of the University of California at Berkeley. "Our Sun is
pretty
average. In any case, you don't need a star exactly like our Sun for
life."
###
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